I have my 35"x12.5" Mickey Tompson MTZ on a 15"x10 steel semi bead lock rim on the tail gate. With a slightly modified factory mount and it is pushing the limits of the fifth door.
A five gallon gas tank, full, would weigh around 50#'s. The tire I have is around 120#'s and I am going to move the tire inboard before something happens.
Try to get a swing out tire mount that might handle the extra load of the tank and tire.